Almost certainly coral, well done. If it was found on the Isle of Man it would be Palaeozoic in age, probably Carboniferous, bu if you tell us exactly where you found it it made be easier to provide an age.

Thanks for the replies everyone. The rock was found 2 years agon on the North West coast of the Isle of Man (near Cronk). I've added another couple of photos with scale to aid identification, which includes the "bottom" of the rock. Any further comments would be great - thank you!